(1) Field of the Invention
The present invention relates to alkenoic acid compounds which are inactivators of dehydropeptidases. In particular, the present invention relates to alkenoic acid compounds which contain a 2-halo ethylene or cyanomethylene substituted carbonyl functions which serve as mechanism-based inactivators for the said enzymes.
(2) Prior Art
Thienamycin and certain thienamycin derivatives (J. Antibiot 32, 1 (1979); J. Am. Chem. Soc. 100, 6491 (1979); J. Med. Chem. 22, 1435 (1979)), known collectively as carbapenems, are broad spectrum beta-lactam antibacterial agents. These antibiotics are stable towards the action of microbial beta-lactamases, the enzymes that traditionally catalyze the hydrolytic breakdown of beta-lactam antibiotics. However, they were shown to be hydrolyzed by mammalian renal dipeptidases (dehydropeptidase I, EC 3.4.13.11). As the product(s) of the enzymic turnover of carbapenems lack antibacterial property (Antimicrob Agents Chemother. 22, 62 (1982)), there exists a need for specific inhibitors/inactivators for these enzymes. The inhibitor could be used in clinical preparations in conjunction with carbapenems, with the expectation that it would inhibit renal dipeptidase, thereby allowing for prolonged availability of the antibacterial agent in vivo. One reversible inhibitor, cilastatin, has been introduced into clinical use recently and is one of a series of alkenoic acid compounds described by Graham et al (J. Med. Chem. 30, 1074 (1987)). Considerably higher levels of dehydropeptidase activity have been noted in tumors (J. Natl. Cancer Inst. 7, 51 (1946)) and in cases of liver disease (Advances in Enzymology and Related Subjects of Biochemistry 8, 117 (1948)), therefore inhibitors of this enzyme could have antineoplastic properties as well. In addition, as microorganisms possess similar enzymes, these inhibitors could be antimicrobial agents. Thus, such inhibitors are of considerable interest.
Renal dipeptidase belongs to a class of hydrolytic enzymes referred to as metalloproteases or metallopeptidases. These enzymes sequester a catalytically important metal in their active sites. The significant metal in vivo appears to be zinc. The porcine (Methods Enzymol. 19, 722 (1970)) and the human renal dipeptidase (J. Biol. Chem. 259, 14586 (1984)) have been purified and shown to have similar catalytic properties. The enzyme is a dipeptidase that requires an L-amino acid at the N-terminus, however, it accommodates L-, D- or dehydro amino acids at the C-terminus. A necessity for the presence of a free amino group at the N-terminus of peptide substrates has been documented, albeit that requirement is absent for unsaturated peptides of dehydroalanine (Advances in Enzymology and Related Subjects of Biochemistry 8, 117 (1948)).
In the design of compounds with potential biological properties, specificity of targeting is of utmost importance. One class of such molecules that often afford very high specificity in inhibiting their targeted enzymes are mechanism-based inactivators ("suicide substrates"). These molecules possess structural elements that are recognized by the target enzyme, allowing for the binding of the molecule to the enzyme active site with high affinity. Subsequently, the enzyme carries out a chemical transformation that results in the formation of an electrophilic species. Since amino acid residues with nucleophilic functionalities often exist in the active sites of enzymes, the electrophilic species may modify such active site residues covalently. The enzyme, modified in the active site, is inactivated irreversibly and is incapable of catalytic turnover (Silverman, R. Mechanism-Based Enzyme Inactivation: Chemistry and Enzymology, CRC Press, Boca Raton, pp 3-12, 1988). Both molecular recognition for initial non-covalent binding of the inhibitor by the enzyme to give the enzyme-inhibitor complex (EI), and the enzyme-mediated chemical transformation of EI work in concert to afford irreversible inactivation of the targeted enzyme with high specificity.